As it is known in the art, patients suffering from kidney failure or renal insufficiency, or patients suffering of particular pathologies should be submitted to specific treatments. More in detail, it is known to treat blood of a patient in an extra-corporeal circuit in order to carry out ultrafiltration, haemodialysis, haemofiltration, haemodiafiltration, plasmapheresis, blood component separation, blood oxygenation, or other treatments. Extra-corporeal blood treatment means taking the blood from a patient, treating the blood outside the patient, and eventually returning the treated blood to the patient. Normally, blood is removed from a blood vessel, through a withdrawal or arterial line of an extra-corporeal circuit, passed through a blood-treating unit and returned to another or to the same blood vessel by a venous line. Extra-corporeal blood treatment is typically used to extract undesirable matter or molecules from the patient's blood, and/or to add beneficial matter or molecules to the blood. Extra-corporeal blood treatment is used with patients incapable of effectively eliminating matter from their blood, for example in the case of a patient who is suffering from temporary or permanent kidney failure. These and other patients may undergo extra-corporeal blood treatment to add to or to eliminate matter from their blood, to maintain an acid-base balance or to eliminate excess body fluids, for instance.
Extra-corporeal blood treatment is typically, but not necessary, performed by sampling the patient's blood in a continuous flow, by introducing the blood into a primary chamber of a treatment device or filter in which the blood comes into contact with a semi-permeable membrane. The semi-permeable membrane selectively lets the unwanted matter contained in the blood pass through the membrane, from the primary chamber to the secondary chamber, and also selectively lets the beneficial matter contained in the liquid going into the secondary chamber pass through the membrane to the blood going into the primary chamber, according to the type of treatment. Generally the same machine may perform a number of different extra-corporeal blood treatments. In ultrafiltration (UF) treatment, the unwanted matter and excess water are eliminated from the blood by convection through the membrane in the secondary chamber. In haemofiltration (HF) treatment, the blood comes into contact with the semipermeable membrane as in UF, and the beneficial matter is added to the blood, typically by the introduction of a substitution fluid into the blood, either before, or after its passage through the filter and before it is returned to the patient. In haemodialysis (HD) treatment, a secondary fluid containing the beneficial matter is introduced into the filter's secondary chamber. The blood's unwanted matter and the excess water cross the semi-permeable membrane and are removed by/with the exhaust secondary fluid, and the beneficial matter of the fresh secondary fluid may cross the membrane the other way round and penetrate into the blood.
In haemodiafiltration (HDF) treatment, the blood and the secondary fluid exchange elements as in HD, and further, matter is added to the blood, typically by introducing a fluid into the treated blood before it is returned to the patient as in HF, and the unwanted matter is also eliminated from the blood by convection. In each treatment, the secondary fluid goes through the filter's secondary chamber and receives the blood's unwanted matter and excess water crossing the membrane. This liquid is then extracted from the filter: it is commonly called waste, and is sent to a drain or to a bag then intended to be discharged into a drain. In fluid transport lines of medical devices, pumps are usually used in order to pump different fluids, such as blood, treatment liquids, waste liquids, along the transport lines. Such pumps may be for example positive displacement pumps (peristaltic pumps), volumetric pumps, piston type pumps, syringes, etc.
One aspect of known extra-corporeal blood treatments is determination and control of various treatment parameters during blood treatment, since it may be useful for the quality of the medical treatment if each treatment parameter remains between maximum and/or minimum threshold values in a correct relation with each other. In fact, deviations in treatment parameters may impair the quality of the medical treatment. Examples of treatment parameters that may be monitored include, but are not limited to: fluid flow rates in different lines of the circuit, ionic dialysance of the dialyzer, clearance of the dialyzer, water permeability (UF coefficient) of the dialyser membrane, blood pressure drop of the dialyzer, etc. It is known to provide medical devices with sensors and control means that allow respectively to measure and to monitor various treatment parameters, and it is known to configure the control means to carry out a specific action, like providing an alarm (for example a sound and/or a message) if a predetermined treatment parameter deviates from a normal value (e.g., above a certain limit). It is to be noted that the values assumed by various parameters during an extra-corporeal blood treatment depend upon many different aspects, including the type of dialyzer, the type of pump and the pump rate, the type and number of further components mounted in the circuit, the specific patient undergoing the treatment, and also further aspects.
Known methods and apparatuses for controlling treatment parameters are often not sufficiently precise, since the variability of the parameters due to the above different factors influence the reliability of the control and may lead to false alarms and/or to lack of alarm in potentially harmful situations.